[SCons] Add configuration for Sphinx options

The default will exit the Sphinx build with error code 1 if any warnings
are encountered, but it will print all the warnings from a single run.

Since all the warnings from Sphinx are now resolved, this change means
that any CI failures due to warnings from Sphinx should be fixed before
merging a pull request.

SConstruct

@@ -258,6 +258,7 @@ defaults.debugLinkFlags = ''
 defaults.noDebugLinkFlags = ''
 defaults.warningFlags = '-Wall'
 defaults.buildPch = False
+defaults.sphinx_options = '-W --keep-going'
 env['pch_flags'] = []
 env['openmp_flag'] = ['-fopenmp'] # used to generate sample build scripts
 
@@ -439,6 +440,12 @@ config_options = [
         'sphinx_cmd',
         """Command to use for building the Sphinx documentation.""",
         'sphinx-build', PathVariable.PathAccept),
+    (
+        "sphinx_options",
+        """Options passed to the 'sphinx_cmd' command line. Separate multiple
+           options with spaces, for example, "-W --keep-going".""",
+        defaults.sphinx_options,
+    ),
     EnumVariable(
         'system_eigen',
         """Select whether to use Eigen from a system installation ('y'), from a

doc/SConscript

@@ -110,7 +110,7 @@ if localenv['sphinx_docs']:
 
     sphinxdocs = build(localenv.Command('${SPHINXBUILD}/html/index.html',
         'sphinx/conf.py',
-        '${sphinx_cmd} -b html -d ${SPHINXBUILD}/doctrees ${SPHINXSRC} ${SPHINXBUILD}/html'))
+        '${sphinx_cmd} ${sphinx_options} -b html -d ${SPHINXBUILD}/doctrees ${SPHINXSRC} ${SPHINXBUILD}/html'))
     env.Alias('sphinx', sphinxdocs)
     env.Depends(sphinxdocs, env['python_module'])